Inkjet Printing of Ag and Polystyrene Nanoparticle Emulsions for the One-Step Fabrication of Hydrophobic Paper-Based Surface-Enhanced Raman Scattering Substrates

Abstract

Hydrophobic substrates for surface-enhanced Raman scattering (SERS) of adsorbate species are of great interest in chemical analysis because they can concentrate the analyte molecules in a small area of the surface, thereby improving the SERS sensitivity. Here, we propose a general strategy to fabricate hydrophobic paper-based substrates for SERS applications. The paper substrates have been manufactured by inkjet printing of aqueous emulsions containing Ag and polystyrene (PS) colloidal nanoparticles. In a first stage, the SERS performance of the substrates was optimized by varying the relative amounts of polymer/metal colloidal nanoparticles, the number of printing layers, and the degree of hydrophobicity of the substrates, using crystal violet as a molecular probe, which is well known for its strong SERS activity. In these conditions, the strongest surface Raman enhancement was observed for the highest water contact angle (146°) achieved. The selected Ag/PS-coated paper substrates showed wide applicability for several analytes, but in this study, a detailed analysis is provided for the pesticide thiram as a proof of concept. Several samples spiked with thiram have been analyzed by SERS, giving a detection limit of 0.024 ppm thiram in mineral water and apple juice, while in apple peel, the detection limit achieved for the same pesticide was 600 ng/cm2. We suggest that this one-step fabrication method produces a hydrophobic coating whose nanoscale features improve the SERS performance of the paper substrates.

Colloidal nanomaterials for water quality improvement and monitoring

“…It should be noted that this approach is not limited to common office paper; other substrates can be coated either varying the emulsion composition or the metal colloids used in the inkjet printing process, as illustrated in Figures 8A-C. The applicability of these substrates using different aqueous Frontiers in Chemistry frontiersin.org matrices was evaluated, such as in the SERS detection of thiram (LOD 0.024 pm) in spiked samples of mineral water and apple juice (Figure 8E) (Martins et al, 2021).…”

“…Several methods for fabricating SERS substrates rely on the adaptation of available technologies for routine applications. Among such methods, inkjet printing has also been explored to produce substrates for SERS detection of water pollutants ( Yu and White, 2010 ; Dai et al, 2014 ; Restaino et al, 2017 ; Godoy et al, 2020 ; Martins et al, 2021 ). This technique has several advantages such as simplicity, low-cost and suitability for large-scale production of substrates.…”

Plasmonic Core–Shell–Satellites with Abundant Electromagnetic Hotspots for Highly Sensitive and Reproducible SERS Detection

“…The SERS signal enhancement from PCSSs is in agreement with the FDTD simulation results, showing more intense hotspots generated by the Al 2 O 3 shell, providing a 3 nm spacing between the Ag core and satellite. Another important factor influencing the enhancement of SERS performance is the increase in the hydrophobic nature of the PCSS nanostructures by rapidly concentrating the R6G molecules within a smaller area of the substrate [43,44]. In order to quantitatively compare the performance of SERS for three different samples, the enhancement factor (EF) was estimated according to the equation EF = (I sers / C sers ) / (I ref / C ref ), where I sers and I ref are the intensities of the Raman peaks of R6G molecules adsorbed on SERS and the reference substrate (SiO 2 /Si), respectively; C sers (10 −6 M) and C ref (10 −2 M) are the concentrations of R6G molecules on SERS and the reference substrate, respectively.…”

Ink-lithographic fabrication of silver-nanocrystal-based multiaxial strain gauge sensors through the coffee-ring effect for voice recognition applications

“…This impediment significantly limits multiaxial sensitivity and conformal contact on human skin, such as on vocal cords. However, inkjet printing can be adopted as a potential solution for these problems because it directly and selectively extracts the NC ink for patterning in the absence of harsh conditions [ 17 – 19 ]. Unfortunately, the device performance can be reduced because the NCs in the ink are susceptible to agglomeration or sintering owing to their low colloidal stability [ 20 , 21 ].…”